High-energy cosmos is violent with hint of dark matter

The highest-energy map of the entire sky is part mayhem, part mystery. Created by NASA’s Fermi space telescope, it reveals hundreds of examples of the most violent and explosive objects in the universe, plus a hint of mysterious dark matter.

For five years, the Fermi Large-Area Telescope has been in orbit around Earth, scanning the sky for gamma rays with an energy between 10 and 500 gigaelectronvolts – more energetic than any previously seen by satellites, but still too weak to spot from the ground.

The majority of the sources are blazars – distant galaxies with violent, massive black holes at their centres. These black holes are spinning rapidly and shooting out jets of gamma rays and particles that happen to point in our direction. Most of the rest are pulsars, intensely bright and dense neutron stars with immense magnetic fields, spinning and flashing like interstellar lighthouses.

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Dark haze

The haze is somewhat more mysterious&colon; it is largely the result of high-energy cosmic rays, remnants of distant and massive explosions, colliding with gas in our own galaxy. But the Fermi team is seeing more gamma rays at these energies than they would expect – about 30 per cent more.

This could be a hint of dark matter, the mysterious stuff thought to make up 85 per cent of the universe’s matter. According to some theories, dark matter particles are their own antiparticles, colliding and annihilating with each other and producing gamma rays.

“It is certainly what people would love to be able to show, but we’re not at a stage right now where we can definitively show that,” says Lynn Cominsky of Sonoma State University in Rohnert Park, California, an astrophysicist on the Fermi team. “But dark matter is something the Fermi team is working very hard and looking for.”

Fermi is no stranger to the hunt for this strange stuff. In 2012, it detected a spike in gamma rays at 130 gigaelectronvolts, a find that electrified the dark-matter seekers – only for dark matter to be ruled out as the source months later. This year, another Fermi signal first glimpsed in 2010 started to look more like dark matter, as other possible explanations for it were ruled out.